Method of preparing finely divided solid metal salts



United States Patent METHOD OF PREPARING FINELY DIVIDED SOLID NETAL SALTS Jerome Panzer, Roselle Park, and Alan Beerbower, Westfield, N.J., and Francesco Bonmartini, New York, N .Y., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed May 31, 1960, Ser. No. 32,520 Claims. (Cl. 2389) This invention relates to a method of preparing finely divided solid metal salts. Particularly, the invention relattes to a method of preparing finely divided metal salts of inorganic mineral acids and C to 0., fatty acids.

Metal salts such as calcium acetate, trisodium phosphate, calcium sulfate, sodium nitrite, etc. are very desirable in the preparation of fluid lubricants and lubricating greases. Such salts impart to oil, extreme pressure, anti-wear, rust prevention, oxidation inhibition and other desirable properties, depending upon the particular salt used. Because of the insolubility of metal salts of low molecular weight fatty acids and inorganic acid salts, it had been generally necessary to use either surfactants, or more frequently, salts and soaps of higher fatty acids (e.g. C to C fatty acids), as suspending agents to maintain the salt of the invention dispersed in the lubricating oil. Also because commercial salts are rather coarse, when directly dispersed in the lubricating oil, the resulting composition is gritty and has poor structural stability. Because of this, it has become the usual commercial practice to form the salt in situ in the lubricating oil by neutralization of acid with a metal base, in the presence of a dispersing agent or a higher fatty acid. This in situ preparation has several disadvantages. Specifically, it requires long heating periods and very precise control of manufacturing variables to achieve the proper particle size distribution. Furthermore, an exactly neutra l product is diflicult to achieve in large scale preparations. For example, if an excess of metal base is used, the free alkali will tend to react with carbon dioxide of 'the air to form carbonate, which will usually tend to make the lubricant gritty and to form a crust upon storage. On the other hand, an excess of acid will usually impair the structural stability of the lubricant to give it afalse hardness (in the case of greases), which then disappears upon working or upon exposure to shearing stresses. This latter phenomenon is believed to be caused by hydrogen bonding of the free acid, which bonds break upon shearing. If the manufacturing is not very carefully controlled, the particle size of part or :all of the salt may be too large. This, in turn, may make the grease gritty, give rise to sedimentation of fluid lubricants, or reduce the thickening effect or antiwear properties of the salt as compared to a similar lubricant containing a more finely divided salt.

It has now been found that it is possible to preform metal salts of exceedingly fi-ne panticle size (e.g. two microns or less), which preformed salts may then be added cold to a lubricating oil and dispersed therein to form the desired lubricants mentioned above. By this new technique, the long heating time and careful control previously necessary for the in situ formation of salts can be avoided and much finer particle size achieved.

The particle size of salts primarily depends upon two factors. These factors are the rate at which the particle nuclei are formed and the rate at which the nuclei grow. Fastformation of nuclei and minimizing their growth, result in small particle size. Both these factors are offectively controlled by the process of the invention.

Briefly, the technique of the invention involves forming the salt in a solvent in which the salt is extremely insoluble, then recovering the salt by filtering or distillation.

It has been further found that either the acid or base reactants necessary to form the salt, or both, may also be insoluble in the salt forming medium. While it is common to dissolve two reactants in a common solvent medium and recover a precipitate product, it is believed new to use such a technique where one of the reactants is also insoluble in the medium to produce an extremely small particle size precipitate.

By using a solvent in which the product is extremely insoluble, there is no chance for the product to redissolve and reprecipitat-e in larger particles, as can occur even if the precipitate is only slightly soluble in the reaction medium. By using a relatively large amount of solvent as compared to the amount of reactants, there is less chance for growth of particles with the result that finer particles are formed. If the reaction mixture is agitated during the precipitation, particle growth is also inhibited. By carrying out the reaction very slowly, as by slow addition of a reactant to the reaction mass, the further growth of particles already present is inhibited. In sum, by control of all the preceding variables, the finely divided salts of the invention are achieved.

In carrying out the invention, metal salt is precipitated by neutralizing metal base dispersed in a hydrocarbon by slowly adding acid while agitating and constantly removing the Water of the reaction or other byproduct as it forms. The finely divided precipitate is then removed by filtration and dried by heating. The dried material can then be directly incorporated into 'a lubricating oil, preferably by using a minor amount of a surfactant in order to stabilize the resulting dispersion.

An alternate technique :of the present invention comprises adding surfactant directly to the hydrocarbon solvent or forming the surfactant in situ in the oil if it too is a salt, and then repeating the above neutralization procedure. The presence of surfactant will usually result in a gel upon neutralization. If the gel is heated above the critical temperature and pressure of the hydrocarbon solvent, followed by venting to slowly remove the solvent, at the same time maintaining the temperature constant, an aerogel is obtained. This aerogel will crumble easily into very small particles suitable for direct dispersion into lubricating oil to thereby form smooth, stable greases or lubricants. If the gel is used directly as it initially forms in the solvent (i.e. without evaporating the solvent at its critical temperature and pressure) the resulting particles are granular. These granular particles will form a grease having poor stability showing oil separation and breaking down under shearing.

The metal component of the salts of the invention may be any metal. However, for lubricant manufacture the metal will preferably be an alkali metal including sodium, lithium, and potassium or an alkaline earth metal such as calcium, strontium or barium. Metals such as iron and aluminum are also used in lubricants.

Suitable acid reactants for forming the salt include C to C fatty acids such as acetic, propionic, butyric acids and anhydrides; as well as inorganic mineral acids such as phosphoric, hydrochloric, nitric, sulfuric, perchloric, etc.

The base reactants include hydroxides, carbonates, and oxides as well as various organic bases which will react with the aforesaid acids to form the desired salts. Among these latter bases are: alkoxides such as NaOCH and LiOCH H quaternary ammonium compounds such [as (CH NO-H; and other nitrogen bases such as hydrazine and lguanidine. Salts produced from the above reactants include calcium acetate, sodium chloride, trisodium phosphate, etc. i

The reaction medium or solvent should be one in which the product is very insoluble. Suitable solvents include hydrocarbon solvents which can be aliphatic,

aryl, cyclo-alphatic, alkyl, aryl, etc. Examples of such solvents include C to C alkanes such as n-pentane, isohexane; aromatic solvents such as benzene, toluene, etc. In some cases alcohols such as methanol, ethanol, isopropanol, etc. and chlorinated solvents, e.g. chloroform, can be used. If an aerogel is to be formed, the solvent should be volatile and have a critical temperature of less than 700 F., preferably less than 500 F. The only real requirement of the solvent is that it be inert, show no solubility for the precipitate, and in the case of the aerogels be volatile and have a low critical temperature.

The acid and base preferably are used in as exact a stoichiometric ratio as possible, but if the acid is volatile, a slight excess of acid may be used and then later removed by evaporation. The weight of solvent used should be 1 to 20, preferably 3 to times the Weight of the reactants. All of the base reactant, which will usually be insoluble, should be first slurried into the solvent. Then, the acid reactant (which is usually soluble) is slowly added over a period of time of about 0.5 to hours, preferably 1 to 10 hours. Actually longer times may be used but may not be economically feasible. Any water of reaction or other by-product is removed by continuous distillation as it is formed. Agitation of the reaction mixture, provided by any method, is desirable in order to maintain the insoluble reactant slurried and to prevent growth of the salt nuclei. Rapid, vigorous agitation is preferred. When all the acid is added and the reaction is completed, the precipitated salt is removed by simple filtration and dried.

Surfactants which may be used in the techniques of the invention are those which preferably are soluble or dispersible in the solvent and which will effectively main tain the salt dispersed in lubricating oil. Examples of such surfactants include simple metal salts of C to C fatty acids, especially the alkali metal and the alkaline earth metal salts. Specific examples of such surfactant salts include calcium stearate, calcium Wecolate (calcium salts of coconut fatty acids having 7 to 12 carbon atoms) lithium oleate, barium myristate, etc. Other surfactants that may be used include non-ionic and ionic surface active agents which are commercially available under trade-names of: Pluronics, Ethomeens, Ethomids, Ethofats, etc.

Particularly effective surfactants are mono and dialkylolamides of C to C fatty acids. These materials have the general formula:

wherein R is a C to C alkyl group of a saturated fatty acid, R is hydrogen or -ROH, and R is a C to C e.g. C to C aliphatic saturated hydrocarbon radical. The hydroxyl group will generally be attached to the terminal carbon atom, although it may be attached to other carbon atoms of the R" hydrocarbon group. Specific examples of such materials include N,N-di(2-hydroxy ethyl) lauramide; N-2-hydroxy ethyl lauramide; N-6-hydroxy hexyl stearamide and N,N-di (3-hfydroxy propyl) launamide. A commercial material consisting of about 65 wt. percent of N,N-di('2-hydroxy ethyl) l-auramide as the active ingredient and available under the trade-name Nopcogen 12-L was used in several of the examples of the invention.

Once the salt is prepared it may be directly dispersed in the lubricating oil, pre-fenably followed by homogenization to insure thorough mixing. If desired, any of the previously mentioned surfactants may be added while dispersing the salt or, as her-einbefore indicated, the salt may be prepared in the presence of the surfactant.

Lubricating oil compositions that can be prepared with the salts of the invention will contain about 3 to 50, preferably 5 to wt. percent of salt dispersed in oil. The oil can be either mineral oil or a synthetic oil.

Generally, about 0.03 to 10, and preferably .05 to 5 wt. percent, based on the weight of salt, of surfactant will also be present.

Various other additive materials may also be included in the compositions of the invention in amounts of about 0.1 to 10.0 wt. percent, based on the total weight of the composition. Examples of such additives include oxidation inhibitors such as phenyl alpha-naphthylamine, tackiness improvers such as pol-yisobutylene, corrosion inhibitors such as sorbitan monooleate, sodium nitrite and lanolin, dyes, V.I. improvers, thickeners and the like.

The lubricant can be homogenized in a Morehouse mill, a Gaulin homogenizer, etc. If a fluid lubricant is desired, it is generally more convenient to first form a concentrate and then to dilute it with additional oil to form the final product.

The invention will be further understood lowing examples:

by the fol- Example I In a two liter flask were placed 1400 cc. of benzene and 72 gms. of hydrated lime. The mixture was well stirred and heated to reflux to remove any free water present by azeotroping with the benzene and using a Dean-Stark trap. When the material in the flask was completely dry, a solution of 114 gms. of glacial acetic acid in 10 0 cc. benzene was added slowly through a separatory funnel. The rate of this addition was adpusted to permit as much water of reaction to be removed by azeotroping as possible, before adding additional acetic acid solution. A total of 23.5 hours was required for this addition. Subsequently, the mixture was heated until no more water came olf. After cooling, the calcium acetate was filtered and dried at 250 F. The particle size distribution of the calcium acetate was as follows: of the particles had a length under 1 micron, 75% of the particles had a length under 0.2 micron and the width of the particles ranged from 0.01 to 0.1 micron. 5.0 wt. percent of the resulting calcium acetate was incorporated into 94 wt. percent of a coastal distillate lubricating oil of 1200' SSU viscosity at 100 F., using 1 wt. percent of Nopcogen 12L as a surfactant. A stable fluid lubricant resulted which showed no oil separation after a week standing.

Example II That the above technique is general for other inorganic solid salts is demonstrated by its application to the preparation of sodium chloride particles (cubes), all smaller than 2 microns in size as compared to commercial sodium chloride in which the smaller particles are rarely less than 15 microns in size. The product was prepared by passing dry HCl gas into a suspension of sodium methoxide in benzene. Specifically, 350 cc. of benzene, cc. of isopropanol, and 25 gms. of NaOCH were mixed together and heated to reflux to remove any free water that might have been present. Dry hydrogen chloride gas was passed through the mixture over a period of about 2 /2 hours while constantly refluxing. At the end of this time the sodium chloride which formed was filtered from the reaction mixture and then dried by heating to a temperature of 250 F. in an oven for about 24 hours. As mentioned above, the resulting salt had a particle size of less than 2 microns.

Example III A. A mixture of calcium acetate and the calcium salt of coconut fatty acids was prepared by adding dropwise a mixture of 90 gms. glacial acetic acid and 45 gms. Wecoline AAC acids to a vigorously stirred and refluxing mixture of 74.7 gms. hydnated lime in 1500 cc. benzene from which free water had been removed. The Wecoline AAC acids are a mixture of 28 Wt. percent caprylic, 56 wt. percent capric and 16 .Wt. percent lauric acids. Water of reaction was continually removed during the addition of the acids. The precipitate reaction product was filtered and dried at 250 F. The resulting particles were granular and formed a grease with poor stability (oil separation and shear breakdown).

B. The same general procedure of forming the precipitate of A was repeated, but using 700 cc. of pure mpentane instead of benzene, since the critical temperature or pentane is lower. A gel was obtained which was heated in a 3 liter bomb to 400 F. and 500 psi. (critical temperature of n-pentane is 335 F), and the pentane solvent was slowly vented to the atmosphere while keeping the temperature constant. The resulting solvent-free aerogel crumbles to a fine powder Which disperses easily into oil. Upon crumbling, no particles were larger than 2 microns and the particle size dis tribution was substantially the same as obtained in Example I. 25 wt. percent of the crumbled aerogel was mixed into 75 wt. percent of a coastal distillate lubricating oil having a viscosity of 1200 SSU at 100 F. on a 3-roller paint mill. The resulting product was a smooth, uniform, non-gritty grease.

While the preceding examples have illustrated the use of salts prepared by the method of the invention in lubricants, such salts can be used tor a variety of other purposes. Thus the method of the invention can be used to prepare salts for printing inks, paints, cosmetics, fuel oils, oil Well completion fluids, or any other use where metal salts in an extremely finely divided form are desired.

What is claimed is:

1. A method of preparing finely divided particles of a solid metal salt by reaction of a metal base and an acid which comprises dispersing said base in an inert liquid medium in which said salt is insoluble, slowly adding a neutralizing amount of said acid to said dispersion of base over a period of about 0.5 to 20 hours while constantly removing any by-product other than said salt and recovering a salt having a particle size less than about 2 microns, and wherein the weight of said inert liquid medium is about 1 to 20 times the combined weight of said base and said acid.

2. A method according to claim 1, wherein said metal salt is calcium acetate, said metal base is lime and said acid is acetic acid.

3. A method according to claim. 1, wherein said metal salt is sodium chloride, said metal base is sodium methoxide and said acid is hydrogen chloride.

4. A method of preparing finely divided particles of a solid metal salt selected from the group consisting of alkali metal and alkaline earth metal salts of inorganic mineral acids and C to C fatty acids, by reaction of a metal base and an acid which comprises, forming a dispersion of said base in an inert liquid medium in which said salt is insoluble, slowly adding a neutralizing amount or" said acid to said dispersion over a period of 0.5 to 20.0 hours while agitating said dispersion and constantly removing any by-product other than said salt by distillation, and filtering said reaction mixture to recover a salt having a particle size less than about 2 microns, and wherein the weight of said inert liquid medium is about 1 to 20 times the combined weight of said metal base and said acid.

5. A method of forming finely divided particles of a solid metal salt which comprises dispersing lime in an inert liquid hydrocarbon solvent, slowly adding a neutralizing mixture of acetic acid and C7 to C acid in a weight ratio of about 2 to 1 to said dispersion over a period of about 1 to 10 hours while constantly removing water of reaction to thereby obtain a gel, heating said gel above the critical temperature of said hydrocarbon solvent and slowly venting said solvent from said gel, recovering a solvent free aerogel and crumbling said aerogel to a powder having a particle size of less than 2 microns, and wherein the Weight of said solvent is about 3 to 15 times the combined Weight of said base and said mixture of acids.

References Cited in the file of this patent UNITED STATES PATENTS 1,916,457 Behrman July 4, 1933 2,739,121 Kronberg et a1. Mar. 20, 1956 2,895,990 Larrison et al. July 21, 1959 2,927,892 Morway Mar. 8, 1960 

1. A METHOD OF PREPARING FINELY DIVIDED PARTICLES OF A SOLID METAL SALT BY REACTION OF A METAL BASE AND AN ACID WHICH COMPRISES DISPERSING SAID BASE IN AN INERT LIQUID MEDIUM IN WHICH SAID SALT IS INSOLUBLE, SLOWLY ADDING A NEUTRALIZING AMOUNT OF SAID ACID TO SAID DISPERSION OF BASE OVER A PERIOD OF ABOUT 0.5 TO 20 HOURS WHILE CONSTANTLY REMOVING ANY BY-PRODUCT OTHER THAN SAID SALT CONSTANTLY REMOVING ANY BY-RODUCT OTHER THAN SAID SALT AND RECOVERING A SALT HAVING A PARTICLE SIZE LESS THAN ABOUT 2 MICRONS, AND WHEREIN THE WEIGHT OF SAID INERT LIQUID MEDIUM IS ABOUT 1 TO 20 TIMES THE COMBINED WEIGHT OF SAID BASE AND SAID ACID. 